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[Paul Spencer] While I'm not an authority on horn design, I present what I'm learning while in the process of attempting to design an effective and compact bass horn. ==== 1. Compile a list of drivers which appear suitable ==== It appears that its possible to design a narrow bandwidth horn for most drivers, however, in general, drivers with an xmax of 12mm, a light moving mass (mms), a fairly low Qts and high BL are preferred. Look for TS parameters that are required by Horn Response ==== 2. Enter parameters, then use Hypex Designer as a starting point ==== In the Tools menu, select "Hypex Designer" and enter in the bandwidth over which you want the horn to be optimised. In my case I choose 40 - 80 Hz ==== 3. Check compression ratio ==== This is the ratio of SD:throat area. If the throat is half SD, then you have a compression ratio of 2, which appears to be a commonly recommended maximum. Often you will get a higher ratio from the Hypex designer, so you may wish to increase throat area. Then you will notice that the response will change ==== 4. Downsizing ==== This is where you start to compromise. If you plan to make a stack of horns, you might reduce mouth size by half and stack two together. Avoid shortening the horn length too much, as this will mean you will lose bottom end and there will be a dramatic loss of performance. ==== 5. Tweaking ==== You may not have a very flat response. If at the bottom of the response there is a peak followed by a trough, you can tweak this with the rear chamber volume (VRC) and throat area (S1). Experiment with this and you will find you can often smooth the bottom end fairly easily. Try changing one thing at a time, then "calculate." Press F4 while looking at the charts for SPL and displacement and you will see the previous version. Change the horn length (HYP) and you will notice that this changes the corner frequency above which it rolls off. Change VRC and you will notice it affects excursion below fc (cut off frequency), as well as the steepness of the rolloff slope. ==== 6. Check excursion and power ==== Double click on "ES" where you enter input power in Volts RMS. It will calculate volts when you enter in impedance and power. For a max SPL check, enter in the nominal power rating of the driver then "calculate." Most likely, you will be well below xmax above fc, but exceed it below fc where excursion increases rapidly. If you use a high pass filter with an fc @ F3, the excursion will decrease approx 30% at that point. If you use a 2nd order high pass, then half an octave below fc the excursion will be reduced by at least half. After such a high pass filter is used, the excursion limited power will increase so that the power handling will be limited by excursion at fc. The actual power handling will be typically 140% of the excursion limited power hanlding at the F3 point without the filter. Example: Suppose you use a driver with an xmax of 10mm in a horn with an F3 at 40 Hz, crossing to a subwoofer below this point with a 2nd order high pass filter. Driver reaches xmax @ 40 Hz with 100w without the crossover. When the crossover is used, the power handling will be 140w. Above this point, the power handling will be thermally limited. Horn loading increases the impedance and less current goes through the voice coil. The driver will fail due to overheating rather than overexcursion in this range. = next [Bass Horn FAQ] = |